A pull-on disposable diaper, which includes an absorbent assembly and an outer cover forming the outer surface of a garment and in which both lateral side edge portions of the outer cover in a front body portion and both lateral side edge portions of the outer cover in a back body portion are joined to each other to form a pair of side seals, is known as a pull-on garment in the related art.
Generally, when a wearer removes a pull-on disposable diaper from a wearer's body, the wearer pulls the side seal to tear the diaper into the front body portion and the back body portion. It is preferable that the side seal is adapted to be capable of being easily torn in order to promptly remove the diaper from the wearer's body when the wearer replaces a diaper after the use of the diaper. In regard to the tear properties of the side seals, for example, Patent Literature 1 discloses an absorbent article in which sides seals have three stages of fusion-bonding strength in terms of compatibility between sufficient fusion-bonding strength that allows the diaper not to be taken off, when a wearer wears the diaper, and the improvement of tear properties.
Further, in the past, a heat roller device has been widely used for the joining of the superposed sheets in steps of manufacturing an absorbent article, such as a disposable diaper or a sanitary napkin, and side seals have been generally formed by a heat roller device as described below. Further, a method for performing fusion-bonding by using a laser beam is also known as other joining methods. For example, Patent Literature 2 discloses a method for fusion-bonding sheets of a sheet-layered body in which a plurality of sheets are superposed by emitting a laser beam to the sheet-layered body from the inside of a rotating roller while deforming the sheet-layered body into a shape along the circumferential surface of the rotating roller, which includes laser beam transmitting portions on the circumferential surface thereof, and transporting the sheet-layered body.
A pull-on disposable diaper is generally manufactured by the following steps. That is, the pull-on disposable diaper is manufactured by: a step of manufacturing a continuous diaper in which a plurality of diapers are lined up in one direction (transporting direction); a step of joining an outer cover of a front body portion side and an outer cover of a back body portion side, which are superposed at portions where the side seals are to be formed, in the continuous diaper by joining means such as a heat roller device; and a step of dividing the continuous diaper into individual diapers by cutting a joined portion of the outer covers with cutting means such as a cutter. Side seals of a conventional pull-on disposable diaper which is manufactured in this way are formed so that lateral side edge portions of the front body portion and the lateral side edge portions of the back body portion are superposed so as to correspond to each other. Since the apex of the superposed portion further protrudes outward from the peripheral portion of the diaper, the apex of the superposed portion can be easily recognized visually.